Variable inductance device



Nov. 5, 1 940. J, w, HAMMOND 2,220,446

VARIABLE INDUCTANCE DEV ICE Filed July 22, 1938 EEE JOHN W. HAMMOND, INVENTOR.

%0 f gg' Patented Nov. 5,

PATENT OFFICE VARIABLE mnuorsncs nnvrcn John w. Hammond, Baltimore, Md., assilnor to Bendix BadioCorpoi-ation, Baltimore, Md, a corporation of Delaware Application July 22,

3 Claims.

This invention relates to a variable inductance device and deals particularly with such a device in which variation of inductance is obtained by rotation of a coil structure.

An object of the invention is to provide an improved construction in which an electrical (5011- tact member is moved along the length of a coil through actuation by rotation of the coil. It is further desired that the electrical contact member be easily'movable along the length of the coil independently of the rotation of the coil.

Another object of the invention is to provide construction in which a resilient brush is held tightly in contact with the coil but wherein the brush is easily slidable lengthwise of the coil without binding or excessive friction. It is desired that the brush be held in place by its own resiliency and be easily removable from the device.

A further object is to provide a brush so constructed that if it should be left out of engagement with a turn of the coil, it will assume its proper engagement with a coil turn upon rotation of the coil.

Yet another object is to provide an improved coil and brush assembly which is simple and inexpensive to construct and which will not easily get out of adjustment.

The improved construction includes a coil structure rotatablymounted in a frame and a brush bar carried by the frame in spaced relation with the coil structure. Carried between the bar and coil structure is a resilient brush member of improved form which is held in flexed position and which engages a turn of the coil so as to he moved along the coil as the coil is rotated.

The improved structure will be more clearly understooci by reference to the accompanying drawing in which- Figure l is a plan view of the impr .completely assembled;

Figure 2 is a view in side elevation, a part of the coil structure being broken away to show the interior construction thereof; a

Figure 3 is a detail view of the improved brush structure, the view being taken as seen from line 3-4 of Figure 2: and

Figure 4 is a. much enlarged sectional view taken at line 4-4 01 Figure 3 and showing the engagement of the brush contact element with a turn of thecoil winding.

As illustrated, A designates a frame; 13, a rotatable coil structure; and C and C2, brushes for making electrical contact at various points along-the length of the coil.

oved device 1938, Serial No. 220,637

The frame A may be of any suitable construction. As here shown, the frame includes a pair of endplates l0 and i I made of insulating material. Extending between endplates l0 and ii are the four bars l2, l3, l4 and i5 which secure and support the endplates in spaced relation. Two of these bars, i2 and I3 in the illustrations given, may be constructed of conducting material and may be known as brush bars since they are used also for confining the brushes in position and for providing electrical connection with the brushes.

Each of bars 12 to I! may have their ends secured to the plates i0 and H by such means as the screws i6 extending through these plates and into the end portions of the bars. Electrically connected to the bars I2 and i3 are the wires i8 and i1. respectively.

The coil structure 13 comprises a cylindrical core piece i9 which on its exterior is provided with a helical groove 20 which receives the turns of the coil winding 2i. At each end of cylinder piece I9 is a core endpiece 22 to which the endshafts 23 and 23* are attached. At the'rear end of the coil structure the endshaft 23 extends rearwardly through the bearing 25 in the frame endpiece i i and makes electrical connection with the wire 25 connected to this bearing. At the front, of the coil structure the endshaft 23 extends forwardly through a bearing in endplate i8 and has its extreme forward end provided with a slot 2% suitable for receiving the tip of a screwdriver for rotating the cell structure. The rear end of the coil winding 2! is connected to a metallic strip Ii which is secured to the endshai't 23. The forward end of. winding 2! may be connected and secured in a similar manner.

bmtsh structure, C, provided in the improved device, is shown in detail in Figures and v inclination with respect to the surface of the coil structure such as shown at 32 and 33 of Figure 4. The end portion of arm 29 is provided 7 with the shoe '34 made of insulating material and extending transversely of arm 29. The shoe 3 should be ofsuflicient length to extend over at least two turns of winding 2i at the several positions of the brush along the coil. At the central portion of the brush are the flanges 35 and 35 which extend laterally oi the arms 28 and 29 and have their end portions 3i and 36* turned upwardly and provided with arcuate recesses 3'! suitable for receiving one of the brush bars l2 or l3 therein.

The brush' C1, as above described, may be inserted into position by placing the end portions of arms 28 and 29 in contact with the winding and depressing the central portion of the brushes and bringing the upwardly extended flange ends 35 and 36 under the bar l2. Then upon release of the central portion of the. brush recesses 8'! in flanges 35 and 36 will engage bar l2 and'the brush will in this way be held against rotation with the coil structure. With the brush in this position, the arms 28 and 29 will be flexed so as to bear-resiliently against the coil winding at their end portions. If the brush element 30 does not happen to receive immediately a turn of winding 2| within its groove 3|, only a slight turn of the coil structure B is necessary to bring this element into proper engaging position with a turn of the winding. This automatic engagement of; a turn of the winding with the groove 3| takes place due to the presence of the bevelled surfaces 32 or 33. It willbe clear that engagement of a coil turn with one of the bevelled surfaces operates to temporarily lift the brush element so as to allow thewinding turn to slip into the groove 3|. The sides of groove 3!, as seen-in Figure 4 of the drawing, are oi sharp inclination so as to avoid disengagement of the winding turn from the groove upon continued turning of the coil structure.

The improved device may be used with the sin.- gle adjustable brush Cl, but if desired another brush C2, of a construction similar to brush C1, may be added to accommodate another circuit. When, as in the illustrated embodiment, two adjustable brushes are employed, one circuit may be connected by the wires I1 and .25, and another circuit may be connected by the wires l8 and 25.

1 Other connecting arrangements may be used as structure B by the use of a screwdriver or other suitable tool inserted in the slot 26 of the endshait 23. For example, when the endshaft 23 is turned in a clockwise direction, each of the brushes C1 and C2, being in engagement with a turn of winding 2|, will be caused to move longitudinally of the coil to increase the number of turns included between .wires l1 and 25, as well as between wires 18 and 25: Turning of the endshaft 23* in a counterclockwise direction operates in a similar manner to decrease the inductance presented by the device in both circuits.

When it is desired to increase or decrease the inductance included between conductors l8 and 25, the operator may simply grasp the arm 28 of the brush C1, and raise the element 30 all the turn of winding 2| with which it-was engaged, and then slide the brush member lengthwise of the coil along bar l2 either to add more turns or decrease the number of turns as may be desired. When the arm 28 is again released at the new brush position, the element 30 will again engage a turn of winding 2| either immediately upon re lease of the arm or upon'the initial rotational movement of the coil in obtaining final adjustment. The position of the brush C: along the coil may also be changed independently of coil rota -a,22o,44e I tion or the position of brush C1, in the manner such as Just described.

The resilient engagement between a turn of winding 2! and one of bars I2 or I3 which is provided by the improved type of brush, makes a very efficient electrical connection between the bar and the winding'since the flexed condition of the brush provides a constant pressure tending to maintain the sliding surfaces in good electrical contact. It is also deemed an advantage that only one of the diverging arms on a brush is in electrical contact with the winding, .if the end portions of both arms of the brush were to be maintained in electrical contact with the winding. It the end portions of both arms of the brush were to be maintained in electrical contact, me-

chanical difllculty would be involved in maintaining alignment of the brush, and also electrical difliculties due to such a bridging arrangement would be involved.

Although only one embodiment of the invention has been illustrated, it is clear that many other embodiments might be constructed. Also many changes may be made in the details of constructionwithout departing from the spirit of the inthe end portion of one of said arms being electrically insulated from said coil, and the end portion of the other of said arms being in electrical contact with saidcoil, said arms being resilient, and means slidably engaging said brush for maintaining said arms flexed and bearing against said coil as the coil is rotated, said last mentioned end portion being'resiliently releasable from engagement with said coil for adjustment along the coil independently of coil rotation.

2. In an inductance device having 'a rotatable coil and being variable by rotation of said coil, a contact brush comprising a piece of resilient material, one end portion of said piece being provided with a coil engaging contact element for making electrical contact with said coil, the other end of said piece being provided with a shoe of insulating material and resting upon said coil, and a bar of conducting material disposed 1ongitudinally of and spaced from said coil, said piece having at its middle portion upwardly extending flanges making slidable engagement with said bar said piece being held in flexed condi-' tion bythe said bar and'coil so as to produce resilient engagement between said brush element and a turn of said coil, said last mentioned engagement being such as to move said piece lonsaid coil.

' JOHN .W. HAMMOND. 

